Diaphragm valves are used in multiple industries. A particular type of diaphragm valve, known as an “air admittance valve,” is used in a wide variety of plumbing systems, such as apartments, schools, and single-family dwellings. For example, an air admittance valve can be installed on a plumbing system to seal unwanted gases escaping from the plumbing system, but allow air into the plumbing system to prevent negative pressure or a vacuum in the system.
Thus, an air admittance valve functions as a special type of one-way valve to seal in one direction at relatively low pressures, but allow in another direction low pressure gas, such as atmospheric air, to pass around the diaphragm through the center of the valve. However, the valve is generally able to sustain a seal at elevated pressures. With these two extremes, the sealing diaphragm must have some special attributes not normally found in typical valves.
The sealing diaphragm is typically not made of a solid material, because it would either be too hard to initially seal at low pressure or too soft to support a seal at high pressure. The diaphragm generally has a soft and very pliable membrane portion for the low-pressure sealing at almost atmospheric pressure and a hard stiff portion for the high-pressure capability. The interface between the very dissimilar materials of a very pliable membrane and the hard stiff portion is the principal area of commercial failure for this type of valve.
One known and commercially available air admittance valve is a Magic Vent™ air admittance valve, widely received in the industry. The valve has a lower portion as a base, an upper portion as a top or dome, and a screen plate placed therebetween. A diaphragm operatively seals against the screen plate in a downward direction and allows flow in an upward direction. The diaphragm generally has at least one hard center disk generally mounted in a horizontal plane with two circular stems extending at angles therefrom. The stems resemble an axel extending from both sides of the horizontal center disk. The stems ride up and down inside guides on the base and dome as the center disk moves up and down in sealing oscillation. A pliable membrane is molded to and extends radially out beyond the periphery of the hard center disk. The extension beyond the center disk effectuates a seal on the screen plate. The diaphragm is permanently mounted within the body of the air admittance valve. Thus, failures generally necessitate replacement of the entire valve.
The failure generally occurs by leakage at the interface between the hard center disk and the pliable membrane molded laterally around the disk. The membrane material has a very soft surface to satisfy the needs of the low-pressure sealing and does not chemically bond with the center disk material when molded thereto. The coupling is primarily mechanical from the molding process. While the assembly performs well, there is room for improvement.
Another solution is to use essentially a two-part screen plate with one hard, generally open framed, subsection (commonly known as a “spider”) that is movable up and down relative to the other part of the screen plate. The diaphragm is a soft, plastic diaphragm and is glued or ultrasonically welded to the spider. The movement of the entire spider and diaphragm assembly effects the seal. The two-step assembly is not cost effective and a single axel design typically allows the diaphragm to tip out of concentric alignment.
Yet another design used by some other commercial manufacturers is to avoid the center disk and membrane design altogether. Instead, the diaphragm is an annular diaphragm and the airflow is reversed inside the body of the valve so that any sealing is done around an annulus, and not through the center of the valve as described above.
Not only do these alternative assemblies raise the costs, but they also provide evidence of the problematic nature associated with these types of valves. Thus, there remains a need for an improved, commercially viable, air admittance valve.